3D echocardiography

Monday, September 6, 2010

Monday, August 30, 2010

CONCLUSION

Three-dimensional echocardiography is a safe, noninvasive

imaging modality that is complementary and

supplementary to 2D imaging and can be used to

assess cardiovascular function and anatomy in various

clinical settings. At present, available evidence suggests

that 3D echocardiography provides improved

accuracy and reproducibility over 2D methods for LV

volume and function calculation and the derivation of

mitral valve area in patients with mitral stenosis. Further

technological improvements and additional clinical

studies will broaden the list of appropriate applications

for this exciting new ultrasound modality.

FUTURE DIRECTIONS

Ongoing developments in 3D echocardiography

include technological innovations and expanding

clinical applications. Automated surface extraction

and quantification, single-heartbeat full-volume

acquisition, transesophageal RT3D imaging,

the ability to navigate within the 3D volume, and

stereoscopic visualization of 3D images are some

of the technological advances that can be expected

over the next several years. These will

further enhance the quality and clinical applications

of 3D echocardiography. In addition, standardized

and focused 3D protocols will be developed

and refined to optimize clinical application

of this technique.

Tagging and/or tracking the LV surface in real

time may provide new approaches to quantifying

myocardial mechanics, such as regional shape and

strain. This approach has great potential and will

complement and likely compare favorably with

the quantitative ability of cardiac MRI. The superior

temporal resolution of echocardiography

should offer unique advantages for this purpose.

In the future, combining the greater temporal

resolution of 3D echocardiography with the excellent

spatial resolution of MRI (or computed

tomography) may yield an imaging data set with

FUTURE DIRECTIONS

Ongoing developments in 3D echocardiography

include technological innovations and expanding

clinical applications. Automated surface extraction

and quantification, single-heartbeat full-volume

acquisition, transesophageal RT3D imaging,

the ability to navigate within the 3D volume, and

stereoscopic visualization of 3D images are some

of the technological advances that can be expected

over the next several years. These will

further enhance the quality and clinical applications

of 3D echocardiography. In addition, standardized

and focused 3D protocols will be developed

and refined to optimize clinical application

of this technique.

Tagging and/or tracking the LV surface in real

time may provide new approaches to quantifying

myocardial mechanics, such as regional shape and

strain. This approach has great potential and will

complement and likely compare favorably with

the quantitative ability of cardiac MRI. The superior

temporal resolution of echocardiography

should offer unique advantages for this purpose.

In the future, combining the greater temporal

resolution of 3D echocardiography with the excellent

spatial resolution of MRI (or computed

tomography) may yield an imaging data set with

Contrast Echocardiography

The use of contrast with 3D echocardiography to

improve quantification of LV volumes offers several

advantages. The RT3D technique (single or

full volume) provides the most practical approach.

Triggering, although not essential, increases

the signal-to-noise ratio and thus is superior

to nontriggered imaging.38 Preliminary

clinical studies have shown promise with regard

to improved LV surface identification and volume

and ejection fraction measurement.129,130

Another evolving application of contrast 3D

echocardiography is in the evaluation of myocardial

perfusion. The ability to record the entire LV

and to quantify the full extent of hypoperfused

myocardium is a potential advantage of this approach.

131-133 However, the problem of microbubble

destruction, even with triggered imaging,

remains a challenge. This is especially true when

matrix array transducers are used, which results in

suboptimal myocardial opacification due to high

acoustic power. Further technological developments

should lead to improvements in all of these

areas and will contribute to more practical applications

of contrast 3D echocardiography.

Intraoperative Applications

The accuracy, feasibility, and value of 3D echocardiography

also have been demonstrated in the

intraoperative environment. Intraoperative 3D

echocardiography provides accurate and often

additional anatomic information compared with

2D transesophageal (TEE) imaging.123 In limited

studies examining 2D and 3D TEE intraoperative

evaluation of mitral valve prolapse anatomy, 3D

TEE evaluation provided complementary and additional

information compared with 2D TEE for

localization of prolapsed scallops (video clip

14).77,124 Intraoperative 3D TEE also has been

used to identify distortion and folding of the mitral

annulus as a cause of functional mitral stenosis or

worsening mitral regurgitation during beatingheart

surgery.125 Finally, intraoperative 3D TEE

has proven valuable in patients undergoing surgery

for congenital heart lesions. For example, the

superiority of intraoperative 3D TEE compared

with 2D has been demonstrated by its ability to

provide en face and oblique views of left atrioventricular

valve malformations in patients undergoing

reoperation for persistent regurgitant lesions

after previous repair of atrioventricular septal

defects.78,126

Intraoperative epicardial RT3D echocardiography

has been used to improve spatial orientation

and assess the extent of septal thickening, mitral

valve systolic anterior motion, and postsurgical LV

outflow tract patency in a patient with hypertrophic

cardiomyopathy undergoing septal myectomy,.

127 It also has been used to guide and monitor

off-pump atrial septal defect closure in a beatingheart

animal model.128 Finally, intraoperative epicardial

and postoperative transthoracic RT3D

echocardiography has been used to evaluate

changes in LV volume and function during cardiac

surgery in patients undergoing infarct exclusion

surgery for ischemic cardiomyopathy.69 In contrast

to 3D echocardiographic imaging, conventional

2D methods may not accurately quantify LV

volumes in patients with severe ischemic cardio

cardiomyopathy,

especially in the presence of significant

geometric changes due to LV aneurysm.

Congenital Heart Disease

Clinical investigations examining the role of 3D echocardiography

in patients with congenital heart disease

have emphasized the unique perspective provided by

3D imaging and the versatility of the technique in

patients with simple defects or complex conditions

and in the postoperative state.115,116 Three-dimensional

echocardiography, using both reconstruction

methods and RT3D, has been used to detect several

forms of congenital heart disease. The ability to record

and analyze the entire cardiac structure and the ability

to display complex spatial relationships are potential

advantages of 3D imaging over 2D echocardiography.

In addition, the decreased examination time afforded

by RT3D echocardiography may reduce the need for

sedation in some children.116

In patients with atrial septal defects, 3D echocardiography

can record the size and shape of the defect. It

also can show the precise location of the defect and

the extent of residual surrounding tissue. In patients

with secundum atrial septal defects (Figure 11, video

clip 13), the extent of the retroaortic rim often determines

the feasibility of repair with percutaneous closure

devices. Three-dimensional echocardiography

also has been used after atrial septal defect closure to

evaluate the success of the procedure and identify the

origin of residual shunting.117 In patients with ventricular

septal defects, the ability to interrogate the entire

septum is frequently cited as an advantage of the 3D

technique.118,119 A novel application of 3D imaging in

patients with ventricular septal defects involves using

offline reconstruction to measure the shape and size of

the color flow jet, which allows for accurate measurement

of the magnitude of shunting in patients with

isolated ventricular septal defects.119

Various 3D echocardiographic techniques have

been used to evaluate RV and LV size and function in

patients with congenital heart disease. The approach

to the LV is similar to that described previously and

permits quantification of dimension, volume, mass,

and ejection fraction.120 Owing to the ellipsoidal shape

of the LV, the advantages of 3D over 2D echocardiographic

techniques are limited, because simple geometric

assumptions can be used to calculate LV volumes;

however, the RV’s asymmetrical shape

invalidates the simple geometric assumptions used for

LV volume calculations. In this case, the ability to

record and analyze the entire chamber rather than

relying on simplifying assumptions has proven

superior.48 In patients with congenital heart diseases

that involve RV pathology, 3D echocardiography correlates

well with MRI for the measurement of RV

volume.48,121,122

Three-dimensional echocardiography has been

successfully applied to the detection and assessment

of several anatomic defects. For example,

the circumferential extent and severity of discrete

subaortic membranes have been successfully visualized

with 3D echocardiography.119,120 With the

apical view, a unique en face image of the membrane

can be recorded, which permits analysis of

the effective orifice area and the dynamic nature

of the defect. Congenital malformations of the

mitral valve also have been assessed with 3D

echocardiography.80 The complex nature of these

defects can make a thorough anatomic evaluation

difficult. In such cases, the perspective provided

by 3D echocardiography can provide a complete

preoperative assessment of the extent and severity

of the valvular abnormality.

Valvular Heart Disease

The recent widespread availability of RT3D echocardiography

obviates many of the practical limitations of

reconstructive 3D techniques and offers the potential

for greater clinical application for valvular heart disease

both in standard diagnostic evaluation and in

real-time guidance during surgical valve repair. This

technique is ideally suited for assessing valve function

given the nonplanar anatomy of the cardiac valves and

the associated anatomic and spatial alterations associated

with valvular heart disease.

Mitral Valve. The 3D echocardiography technique

has contributed significantly to our understanding of

mitral valve function and anatomy. The mitral valve is

particularly suited to 3D assessment because of the

complex interrelationships among the valve, chordae,

papillary muscles, and myocardial walls. This technique

can provide important insight into mitral valve

structure, demonstrating the saddle shape of the mitral

annulus, with high points located anteriorly and low

points oriented in a mediolateral direction (Figure 10,

video clip 8). This has helped clarify the appropriate

diagnostic imaging planes from which mitral valve

prolapse should be diagnosed, thereby avoiding falsepositive

interpretations.64,65

In addition, 3D echocardiography has provided important

mechanistic insights into functional and ischemic

mitral regurgitation resulting from derangements

of the normal spatial relationships of the mitral valve

leaflets to its chordal attachments, papillary muscles,

and the LV.13,66 Distortion of the normal spatial relationship

between the LV and mitral valve apparatus

results in papillary muscle displacement and tethering

of the mitral leaflets, leading to incomplete closure of

the leaflets and mitral regurgitation (video clip 9). The

3D echocardiography technique has identified

changes in annular shape occurring with functional

mitral regurgitation.67-69 These mechanistic and anatomic

insights based on 3D analysis have provided the

basis for the development of new approaches to

treating ischemic mitral regurgitation.70-74

Three-dimensional echocardiography has been used

to define and localize mitral leaflet lesions in mitral

valve prolapse, endocarditis, and congenital mitral

abnormalities.75-80 This application has been particularly

important in guiding surgical repair (video clips

10 and 11).81-83

The RT3D approach has also demonstrated efficacy

in quantifying mitral regurgitation by using 3D guidance

to directly measure the proximal flow convergence

region.84,85 It has provided insight into how

premitral orifice geometry affects the calculation of

mitral valve area in mitral stenosis.86 Calculation of

mitral valve area by 3D echocardiography has been

demonstrated to be accurate, reproducible, and less

variable than conventional 2D methods

and thus has been recommended as the firstline

method.92 In addition, 3D echocardiography has

been used for guidance during percutaneous mitral

valvuloplasty.93,94

Aortic Valve. Three-dimensional echocardiography

has been applied for anatomic assessment of the aortic

valve and root morphology and to calculate the valve

area in aortic stenosis.95-99 The technique has been

used to delineate aortic flow patterns100,101 and has

demonstrated feasibility and accuracy in quantifying

aortic regurgitation.102,103 Other applications have included

the detection and localization of aortic valve

vegetations, assessment of congenital outflow obstruction

abnormalities, and demonstration of morphological

changes in the valve after balloon dilation.103-107

Tricuspid and Pulmonary Valves. Compared with

the aortic and mitral valves, the tricuspid and pulmonary

valves have been less widely studied with 3D

echocardiography. This technique has demonstrated

anatomic changes with rheumatic and degenerative

tricuspid valve disease.108-110 and has accurately reconstructed

congenital tricuspid valve abnormalities, such

as atrioventricular canal defects.111,112 For the pulmonary

valve, 3D assessment has been limited to descriptive

case reports defining anatomic abnormalities associated

with pulmonary valve stenosis and

endocarditis